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Seed size affects individual fitness in wild plant populations, but its ability to evolve may be limited by low narrow-sense heritability (h2). h2is estimated as the proportion of total phenotypic variance (σ2P) attributable to additive genetic variance (σ2A), so low values of h2may be due to low σ2A(potentially eroded by natural selection) or to high values of the other factors that contribute to σ2P, such as extranuclear maternal effects (m2) and environmental variance effects (e2). Here, we reviewed the published literature and performed a meta-analysis to determine whether h2of seed size is routinely low in wild populations and, if so, which components of σ2Pcontribute most strongly to total phenotypic variance. We analyzed available estimates of narrow-sense heritability (h2) of seed size, as well as the variance components contributing to these parameters. Maternal and environmental components of σ2Pwere significantly greater than σ2A, dominance, paternal, and epistatic components. These results suggest that low h2of seed size in wild populations (the mean value observed in this study was 0.13) is due to both high values of maternally derived and environmental (residual) σ2, and low values of σ2Ain seed size. The type of breeding design used to estimate h2and m2also influenced their values, with studies using diallel designs generating lower variance ratios than nested and other designs. e2was not influenced by breeding design. For some breeding designs, the number of genotypes included in a study also influenced the resulting h2and e2estimates, but not m2. Our data support the view that a diallel design is better suited than the alternatives for the accurate estimation of σ2Ain seed size due to its factorial design and the inclusion of reciprocal crosses, which allows the independent estimation of both additive and non-additive components of variance.

Copper-based nanoparticles have wide application in agriculture as fungicides and bactericides. Due to the rapid increase in their use, it is imperative to understand their environmental impact, especially on agricultural crops. In this study, inductively coupled plasma mass spectrometry (ICP-MS) based metallomics and gas chromatography-time of flight mass spectrometry (GC-TOF-MS) based metabolomics were applied to detect metal and molecular changes in cucumber plants exposed to various environmentally-relevant levels of nano copper (nCu at 0, 200, 400, and 800 mg kg−1) until full maturity. Metallomics studies showed nCu caused the perturbation of Fe uptake in leaves. In fruit, Ca, K, S, P, Zn and Mg increased after exposure to 400 and 800 mg kg−1nCu. Metabolomics and partial least-squares discriminant analysis (PLS-DA) revealed that the metabolite profile in cucumber fruits was distinctively altered due to exposure to nCu. A number of metabolites were either up-regulated (proline, glycine, valine, pelargonic acid, arachidic acid, xylose, benzoic acid) or down-regulated (citric acid, myo-inositol, ornithine, 1-kestose) in response to nCu exposure. Biological pathway analysis showed a number of C and N related pathways were changed, especially galactose metabolism and the tricarboxylic acid cycle, indicating C and N metabolism was perturbed by nCu. This study showed GC-TOF-MS based metabolomics combined with ICP-MS based metallomics provide the necessary preliminary data to conduct further mechanistic investigations.

Despite an increasing number of studies over the past decade examining the interactions between plants and engineered nanomaterials (ENMs), very few have investigated the influence of environmental conditions on ENM uptake and toxicity, particularly throughout the entire plant life cycle. In this study, soil-grown herbaceous annual plants (Clarkia unguiculata) were exposed to TiO2, CeO2, or Cu(OH)2ENMs at different concentrations under distinct light and nutrient levels for 8 weeks. Biweekly fluorescence and gas exchange measurements were recorded, and tissue samples from mature plants were analyzed for metal content. During peak growth, exposure to TiO2and CeO2decreased photosynthetic rate and CO2assimilation efficiency of plants grown under high light and nutrient conditions, possibly by disrupting energy transfer from photosystem II (PSII) to the Calvin cycle. Exposure Cu(OH)2particles also disrupted photosynthesis but only in plants grown under the most stressful conditions (high light, limited nutrient) likely by preventing the oxidation of a primary PSII reaction center. TiO2and CeO2followed similar uptake and distribution patterns with concentrations being highest in roots followed by leaves then stems, while Cu(OH)2was present at highest concentrations in leaves, likely as ionic Cu. ENM accumulation was highly dependent on both light and nutrient levels and a predictive regression model was developed from these data. These results show that abiotic conditions play an important role in mediating the uptake and physiological impacts of ENMs in terrestrial plants.

The possibility that sexual selection operates in angiosperms to effect evolutionary change in polygenic traits affecting male reproductive success requires that there is additive genetic variance for these traits. I applied a half‐sib breeding design to individuals of the annual, hermaphroditic angiosperm, wild radish (Raphanus raphanistrum: Brassicaceae), to estimate paternal genetic effects on, or, when possible, the narrow‐sense heritability of several quantitative traits influencing male reproductive success. In spite of significant differences among pollen donors with respect to in vitro pollen tube growth rates, I detected no significant additive genetic variance in male performance with respect to the proportion of ovules fertilized, early ovule growth, the number of seeds per fruit, or mean individual seed weight per fruit. In all cases, differences among maternal plants in these traits far exceeded differences among pollen donors. Abortion rates of pollinated flowers and fertilized ovules also differed more among individuals as maternal plants than as pollen donors, suggesting strong maternal control over these processes. Significant maternal phenotypic effects in the absence of paternal genetic or phenotypic effects on reproductive traits may be due to maternal environmental effects, to non‐nuclear or non‐additive maternal genetic effects, or to additive genetic variance in maternal control over offspring development, independent of offspring genotype. While I could not distinguish among these alternatives, it is clear that, in wild radish, the opportunity for natural or sexual selection to effect change in seed weight or seed number per fruit appears to be greater through differences in female performance than through differences in male performance.

Competition among many microgametophytes for a limited number of ovules can lead to both nonrandom fertilization by pollen genotypes and selection for greater sporophytic vigor. The evolutionary implications of this process depend on the extent of heritable genetic variation for pollen competitive ability. Using flower color in wild radish as a genetic marker, we demonstrate differences among pollen donors in competitive ability. Significant differences were found in four out of five pairs of donors. For three pairs of donors, competitive differences were observed in certain maternal plants but not others. To test for heritability of pollen performance, we conducted a selection experiment. We manipulated the intensity of pollen competition for two generations and then tested for differences in the performance of pollen from two selected lines. Competitive ability of pollen derived from each line was assessed relative to a standard unrelated pollen donor, using pollen mixtures on six wild maternal plants. The intensity of previous pollen competition had no overall effect on the proportion of seeds sired by each selected line. In two maternal plants, pollen from intense previous competition was actually inferior, contrary to expectation. Thus, we found no evidence for heritable variation in this trait. Other factors, such as male‐female interactions, may influence the outcome of pollen competition. Prevailing theory on the genetic basis of effects of pollen competition on subsequent generations is not supported by our results. Improved protocols for future experiments are discussed.

To determine the effects of density, genotype, and their interaction on individual seed mass in Raphanus sativusL., we replicated maternal and paternal families of seed across two planting densities in an experimental garden. Seeds were produced by a nested breeding design performed in the greenhouse. Among garden‐raised plants, density had a strong negative effect on the mass of seeds produced. At low density, the identity of the greenhouse‐grown maternal plants had a strong effect on F2seed mass, while in high‐density plots, there were no significant parental effects on mean seed mass. Significant parental genotype density interactions contributed to variation in F2seed mass. Norms of reaction for each of the 15 paternal sibships illustrate paternal family density interactions. Three sibships exhibited significant declines in mean seed mass with increasing density; 12 sibships showed no change. Maternal family density interaction effects on seed mass were also detected; among maternal sibships, mean seed mass at low density was negatively correlated with mean seed mass at high density. These results demonstrate: a) planting density has a strong effect on mean individual seed mass produced by adults; b) density influences the magnitude of maternal effects on progeny phenotype; and c) genotype density interactions influence seed mass, potentially contributing to the maintenance of maternal genetic variation in seed mass in natural populations of wild radish.

Seed weight varies significantly within and among fruits of wild radish (Raphanus raphanistrum). To determine sources of this variation, we studied fertilization and seed development following controlled pollinations. Within fruits, central ovules were fertilized prior to distal ovules and attained greater seed size. Ninety‐seven percent of the variation in mean seed wt per fruit was explained by an analysis of variance incorporating parental effects, pollination date, and the number of seeds per fruit. We document strong maternal effects on the number of ovules per ovary, the number of fertilized ovules per ovary, the number of seeds per fruit, and mean individual seed wt per fruit. Across females, pollen donor had a slight but significant effect on seed wt; no paternal effects on fertilization rate, zygote number, or seed number per fruit were detected. Within females, with one exception, pollen donor had no significant effect on these components of seed development. Stronger maternal main effects may be due to donor x recipient interactions, cytoplasmic factors, the genetic inequity within triploid endosperm, and/or strict maternal control over resource allocation. The large maternal effects relative to paternal effects may limit the rate at which natural selection acts on paternal traits expressed prior to seed maturation.

To determine the effect of growing conditions on population parameters in wild radish, (Raphanus sativusL.: Brassicaceae), we replicated maternal and paternal half‐sib families of seed across three planting densities in an experimental garden. A nested breeding design performed in the greenhouse produced 1,800 F1seeds sown in the garden. We recorded survivorship, measured phenotypic correlations among and estimated narrow‐sense and broad‐sense heritabilities (h2) of: days to germination, days to flowering, petal area, ovule number/flower, pollen production/flower, and modal pollen grain volume. Survivorship declined with increasing density, but the relative abundances of surviving families did not differ significantly among densities. Seeds in high‐density plots germinated significantly faster than seeds sown in medium‐ or low‐density plots, but they flowered significantly later. Plants in high‐density plots had fewer ovules per flower than those in the other treatments. Petal area and pollen characters did not differ significantly among densities. Densities differed with respect to the number and sign of significant phenotypic correlations. Analyses of variance were conducted to detect additive genetic variance (Va) of each trait in each density. At low density, there were significant paternal effects on flowering time and modal pollen grain volume; in medium‐density plots, germination time, flowering time and ovule number exhibited significant paternal effects; in high‐density plots, only pollen grain volume differed among paternal sibships. The ability to detect maternal effects on progeny phenotype also depended on density. Narrow‐sense h2estimates differed markedly among density treatments for germination time, flowering time, ovule number and pollen grain volume. Maternal, paternal and error variance components were estimated for each trait and density to examine the sources of variation in narrow‐sense h2across densities. Variance components did not change consistently across densities; each trait behaved differently. To provide qualitative estimates of genetic correlations between characters, correlation coefficients were estimated using paternal family means; these correlations also differed among densities. These results demonstrate that: a) planting density influences the magnitude of maternal and paternal effects on progeny phenotype, and of h2estimates, b) traits differ with respect to the density in which heritability is greatest, c) density affects the variance components that comprise heritability, but each trait behaves differently, and d) the response to selection on any target trait should result in different correlated responses of other traits, depending on density.

We observed norms of reaction for life history and floral traits in Raphanus sativus L. (wild radish: Brassicaceae) among genotypes raised in three planting densities. In the greenhouse, we used a nested breeding design to produce F1seed representing 60 maternal plants and 15 pollen donors grown from field-collected seed. Eighteen hundred seeds were grown in three planting densities in an experimental garden. For each individual, we recorded survivorship, germination date, flowering date, petal area, ovule number, pollen production, and the mode of individual pollen grain volume/ flower. Planting density had a strong effect on survivorship, but differential mortality among genotypes was not density-specific. Two-way ANOVAS (block and density as class variables) were conducted on each paternal sibship to detect significant differences among densities with respect to mean phenotype. Among the 15 paternal genotypes, 12 exhibited significantly faster germination in the high-density plots. Three paternal families exhibited significantly delayed flowering at high-density. Two paternal families exhibited significant effects of density on petal area, but in opposite directions. Two paternal families had significantly lower ovule production at high-density. No paternal families exhibited significant effects of density on pollen production or pollen-grain volume. Strong differences among genotypes with respect to the effects of density on phenotype indicate genetic variation in the plastic response to density for these traits. Three-way ANOVAS of each density treatment measured the effects of block, paternal family and maternal family on phenotype; significant paternal effects indicated the presence of significant additive genetic variance ( VA) in the measured trait. The ability to detect VAand maternal effects nested within paternal genotypes in most of these traits was density-specific.Heredity (1991) 67, 143–156; doi:10.1038/hdy.1991.74

To document seasonal changes in the reproductive behavior of the perfect-flowered, self-incompatible mustard, Raphanus sativus L., we monitored individual survival, flower and fruit production among 58 individuals in a California population over six census dates (cohorts). Population size declined dramatically and mean individual levels of fruit set changed significantly between cohorts. The frequency distribution of flower and fruit production became increasingly skewed over the first four cohorts. The phenotypic maleness of individuals, a standardized measure of phenotypic gender, oscillated during the reproductive season, peaking in the third and fourth cohorts. We calculated a simple estimate of expected male reproductive success of each plant (the number of fruits sired on conspecifics); this estimate was a function of an individual's flower production and the fruit production of its potential mates in our sampled population. Mean expected male success did not differ significantly among cohorts; expected male success per flower did, however, change significantly among cohorts. Among individuals within each cohort, maternal fruit production and expected male success were both positively correlated with flower production throughout the season. Spearman rank correlation coefficients indicate that the strength of these associations, however, changed during the season. Linear regressions of transformed variables indicated that the shape of several fitness functions also changed over time. In addition, the amount of variation in maternal or expected paternal success explained by flower production declined over the first four cohorts. If typical of wild populations, these temporal changes in these functions suggest that measurements of the intensity of phenotypic selection on flower production will depend on when and how fitness is measured in natural populations.

Phenotypic and genetic variation and correlations among floral traits within and among four Primulaspecies were measured to seek evidence for potential constraints on the independent evolution of floral characters, to examine the relationship between mating system, ploidy level, and sex allocation, and to determine whether some traits are more conservative than others within and across these congeners. We measured mean flower diameter, corolla depth, pollen production, modal pollen grain volume, ovule number per flower, and pollen: ovule ratios for 64 field‐collected genotypes from northern Europe. These represented one heterostylous (P. farinosa: 2n =18) and three homostylous (P. scotica:2n =54, P. scahdinavica: 2n =74, and P. stricta:2n~ 126) species. All traits differed significantly among species and among the six taxon/morph categories identified (including three morphs of P. farinosa:pin, thrum, and homostylous). Pollen production per flower was significantly higher (and individual pollen grain volume lower) in the outcrossing P. farinosathan in any of the homostylous species; also, pin morphs produced significantly more pollen per flower than thrums in P. farinosa.Among the homostylous species, there were significant differences in all traits except modal pollen grain volume. Ovule number per flower and flower size were less variable among taxa than pollen production and pollen volume. Within species, there were several strong negative correlations among genets between pairs of traits, but each species exhibited a unique set of inverse relationships. We detected only one significant positive genetic correlation; in P. stricta, ovule number and pollen production per flower were positively correlated among genets. Among species means, two pairs of traits were negatively correlated: mean ovule number per flower vs. flower diameter (but P =0.0587), and mean pollen production per flower vs. modal pollen grain volume. These negative correlations within and among taxa suggest that there may be intrinsic genetic constraints on the independent evolution of these floral characters, but that these constraints differ among species.